This invention relates in general to a pump and in particular to a ball screw pump for use in a pressurized fluid system, including vehicular Antilock/Traction Control/Vehicle Stability Control braking systems.
Vehicles are commonly slowed and stopped with hydraulic braking systems. These systems vary in complexity but a base brake system typically includes a master cylinder, pressure fluid conduit, and a wheel brake cylinder. The master cylinder generates hydraulic forces by pressurizing brake fluid when the driver applies a brake pedal. The pressurized fluid travels through the pressure fluid conduit to actuate the brake cylinders at the wheels and slow the vehicle.
Vehicle braking systems have evolved beyond the base braking system to provide improved brake pressure regulation resulting in increased versatility. Anti-lock Braking Systems (ABS) provide decreased stopping distances and controlled braking under adverse conditions. An ABS system monitors wheel rotational behavior and regulates the brake pressure in the corresponding wheel brakes in order to maintain the wheel speed within a selected slip range while achieving maximum braking forces. A Traction Control (TC) system controls excessive wheel slip during acceleration to improve vehicle traction. A Vehicle Stability Control (VSC) system automatically actuates selective wheel brakes to counteract dynamic forces generated during cornering which improves vehicle stability.
Typical ABS/TC/VSC systems use a motor driven pump to provide pressurized fluid used to actuate the wheel brake cylinders. The pump must provide a sufficient capacity of fluid at high pressure for these braking systems to operate properly. Pump noise is a common problem for pumps meeting the pressure and capacity requirement of vehicle braking systems. A noisy pump can be displeasing to the driver. Additionally, many pumps produce undesirable large pressure pulses which can be felt by the driver.
It would be desirable to provide a pump for use in vehicular braking systems that is quiet and produces a smooth high pressure output without pressure spikes.